A flow-through centrifuge without rotating seals was recently described for on-line plasmapheresis of whole blood. We have redesigned the separation chamber to permit continuous plateletpheresis, leukopheresis and plasmapheresis. The new separation chamber has a single narrow spiral channel (3.5 cm high, 0.45 cm wide, and 100 cm long with a total prime volume of 180 ml) with terminals for the blood inlet and packed RBC outlet, and plasma, WBC and/or platelet outlets. Blood cells sediment in a radially acting centrifugal field (100-340 x g) along a distance of 0.45 cm. In this spiral configuration, blood flows "uphill" against a "g" force gradient which forces heavier to travel in opposite direction to plasma and lighter cells (countercurrent flow), each fraction being continuously harvested through the respective terminal. The device was tested at up to 400 ml/min blood flow rate. Preliminary experiments showed highly efficient separations of plasma, platelets and lymphocytes from the whole blood.